Modern wireless communications systems place great demands on the antennas used to transmit and receive signals. Antennas may be required to produce a radiation pattern with a carefully tailored and well defined beamwidth in azimuth and elevation, while maintaining high gain characteristics and operating over a broad bandwidth. Antennas may be required to transmit and/or receive signals on one or both of two orthogonal polarisations.
A patch antenna is a type of antenna that may typically be used in a wireless communications system such as a fixed wireless access system, for example at a base station or at a user equipment terminal, such as customer premises equipment. A patch antenna typically comprises a sheet of metal known as a patch radiator, disposed in a substantially parallel relationship to a ground plane. There may be a dielectric material between the patch radiator and the ground plane, such as a typical printed circuit board substrate comprising, for example, a composite of glass fibre and resin, or there may be an air dielectric, in which case the patch radiator may be held in position in relation to the ground plane by non-conducting spacers, for example. The patch radiator may be, for example, rectangular with one side of approximately half a wavelength in length at an operating frequency of the antenna, and is typically connected to a radio transceiver by a feed track or tracks of defined characteristic impedance, typically 50 Ohms.
It is convenient to provide the feed track or tracks on one side of the ground plane and to locate the patch radiator on the other side of the ground plane. This allows the ground plane to provide a ground reference for both the patch radiator and the feed tracks, and provides shielding of radiation from the feed tracks. An aperture may be provided in the ground plane, in a so called aperture coupled patch antenna, arranged so that signals are coupled from the feed track or tracks to the patch radiator through the aperture. The ground plane is a thin conductive sheet, typically a copper layer of a printed circuit board, supported by the substrate of the printed circuit board, typically an epoxy-glass composite material. For example, aperture coupled antennas are described in the reference D. M. Pozar, “A Microstrip Antenna Aperture Coupled to a Microstrip Line”, Electronics Letters, Vol. 21, pp. 49-50, Jan. 17, 1985 which describes antennas having thin ground planes formed as a copper layer of a printed circuit board having a dielectric substrate. However, the use of such a ground plane in an antenna assembly may present manufacturing difficulties and limit design options for the assembly.
It is an object of the invention to mitigate the problems of the prior art.